
MOTOROLA
Chapter 7. Reset
7-5
Data Coherency During Reset
7.3
Data Coherency During Reset
The MPC565/MPC566 supports data coherency and avoids data corruption while in reset.
If a cycle is to be executed when detecting any SRESET or HRESET source, then the cycle
will either complete or will not start before generating the corresponding reset control
signal. There are reset sources, however, when the MPC565/MPC566 generates an internal
reset due to special internal situation where this protection is not supported. See
In the case of large operand size (32 or 16 bits) transaction to a smaller port size, the cycle
is split into two 16-bit or four 8-bit cycles. In this case, data coherency is assured and data
will not be corrupted.
In the case where the core executes an unaligned load/store cycle which is broken down into
multiple cycles, data coherency is NOT assured between these cycles (i.e., data could be
corrupted).
A contention on the data pins may occur while asserting external reset (EXT_RESET)if
the data coherency mechanism is required, and thus enables a cycle to complete, while
external hardware drives the data for the configuration word. See
Table 7-2 for a
description of the required EXT_RESET line source in a system.
7.4
Reset Status Register
All of the reset sources are fed into the reset controller. The 16-bit reset status register
(RSR) reflects the most recent source, or sources, of reset. (Simultaneous reset requests can
cause more than one bit to be set at the same time.) This register contains one bit for each
reset source. A bit set to logic one indicates the type of reset that occurred.
Once set, individual bits in the RSR remain set until software clears them. Bits in the RSR
can be cleared by writing a one to the bit. A write of zero has no effect on the bit. The
register can be read at all times. The reset status register receives its default reset values
during power-on reset. The RSR is powered by the KAPWR pin.
Table 7-2. Reset Configuration Word and Data Corruption/Coherency
Reset Driven
Reset to Use for Data Coherency
(EXT_RESET)
Comments
HRESET
SRESET
HRESET
HRESET & SRESET
HRESET || SRESET
Provided only one of them is driven into
the MPC565/MPC566 at a time